The present invention relates generally to apparatus for regulating the speed of rotation of a body, and more specifically to a pulse width correcting or modulating device which provides a train of equally-spaced, speed-related pulses to serve as a speed control signal.
In applications where maintaining a rotating body at a constant speed is of primary concern, a closed-loop control system is provided to compensate for speed variations arising from changes in load. In one application, a speed-related signal is obtained by photoelectrically detecting light-reflective areas or teeth arranged on the circumference of a revolving shaft or body. The signal is in the form of equally spaced pulses at a given speed of rotation, the interval between successive ones of which is inversely proportional to the speed and used to generate a control signal proportional to the pulse interval. However, it is difficult to ensure equal spacing between successive pulses because of the large mechanical tolerances in the manufacture of the light reflecting teeth. unequal pulse spacing will produce a nonuniform control voltage even when the body rotates at a constant speed and can send a false control signal through the feed-back loop.